In the current Universal Mobile Telecommunication System (“UMTS”), R4 compliant mobile stations are supported by a Network Assistant Cell Change procedure. Specifically, for networks that support a Cell Change Notification (“CCN”) mode, upon a mobile station detecting the need to change cells due to deteriorated radio frequency (“RF”) conditions, the network is notified of the proposed cell change with a Packet Cell Change Notification (“PCCN”) message from the mobile station. If the network knows the target cell data, the network responds accordingly by sending one or more Packet Neighbor Cell Data (“PNCD”) messages back to the mobile station. Two general scenarios happen at this point. In one scenario where the network determines that the cell chosen by the mobile station is an optimal cell, the network sends a Packet Cell Change Continue (“PCCC”) message to the mobile station. If, on the other hand, in the second scenario where the network determines that the cell chosen by the mobile station is not an optimal cell, a Packet Cell Change Order (“PCCO”) message is sent to the mobile station. This whole procedure of sending the PCCC or the PCCO message to the mobile station is guarded by a timer of 960 milliseconds. In other words, the network is given 960 milliseconds to respond with the PCCC or PCCO message to the mobile station, counting from the time when the network receives the PCCN message from the mobile station.
The problem is that if the mobile station sends out the PCCN message while the Count Down (“CV”) is starting to decrement, meaning that very little data are left to complete the data transmission between the mobile station and the serving station, the mobile station will, nevertheless, terminate the ongoing Temporary Block Flow (“TBF”) as soon as it receives the PCCC or PCCO message from the network. This is true even when the data transfer could have been finished in less than 960 milliseconds. Similarly, in the downlink example, the mobile station could receive the PCCC or PCCO message when the remaining data could have been transferred within the allowed time. So, instead of finishing the data transfer with the current serving cell, the mobile station starts the data transfer all over again by establishing a new TBF at the target cell to finish transferring the remaining data. Starting a new TBF is very inefficient, however, because it requires a significant amount of time, especially when the data transfer could have been finished in less than 960 milliseconds. Another problem is that if the data transfer involves the Transmission Control Protocol (“TCP”) layer that requires an acknowledgement (“ACK”) packet, this ACK packet can be further delayed, because the mobile station is forced to leave the current cell and establish a new TBF in the target cell to finish the data transfer. This again is very efficient. Thus, for all these reasons, the overall data transfer rate of the mobile station is reduced, resulting in deterioration of mobile station overall performance.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of various embodiments of the present invention. Also, common and well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.